The present invention relates to an apparatus and method for measuring the width of a gap of a non-conductive material between conductive materials of a sample such as a magnetic head of a magnetic recording apparatus, and more particularly to an apparatus and method for measuring the width of a micro gap not larger than 0.2 .mu.m which has been impossible to measure by an optical measuring apparatus hitherto.
The width of a gap of a magnetic head has been decreased more and more as the recording density of magnetic recording apparatus, for example, video disks, hard disks, etc. have been improved. This has been accompanied by an increased need to measure the reduced width of the gap in the development/inspection process of the magnetic head.
An example of a conventional method for measuring the width of the gap will be described hereinbelow with reference to FIG. 6.
FIG. 6 illustrates a conventional measuring method for measuring the gap width. In the drawing, reference numeral 101 represents a measuring sample; 102 an objective lens; 103 a body of a microscope; 104 a light source; 105 a CCD camera; 106 a computer; 107 an XYZ stage; and 108 a gap formed in the sample 101.
The operation for measuring the width of the gap in the conventional method will now be described.
The gap 108 illuminated by the light source 104 is magnified with the magnification not smaller than 1000 times by the CCD camera 105 via the objective lens 102 and the microscope body 103. The image magnified by the CCD camera 105 is processed by the computer 106, to thereby measure the width of the gap 108.
The width of a gap not larger than 0.2 .mu.m has been measured conventionally in the following two methods.
FIG. 7 is a diagram of signals along the direction of the gap detected by the CCD camera 105. In an optical system using a xenon lamp of the wavelength .lambda.=350 nm as a light source, even when an objective lens showing NA=0.9 is employed, the limit of the separable width is .lambda./(2*NA)=350 nm/(2*0.9)=194 nm. As is apparent from FIG. 7, the signal indicative of the gap is not dependent on the width of the gap if the gap is not larger than 0.2 .mu.m and the intensity of the output signal alone is changed. Therefore, a reference sample should be polished to assume the reflectivity optically the same as that of the measuring sample and then, the width of the gap not larger than 0.2 .mu.m is measured by the intensity of the signal.
In the conventional arrangement, since the limit of the separable width is 194 nm when the optical system using the generally available xenon lamp of the wavelength .lambda.=350 nm is used, it is impossible to accurately measure the gap width not larger than 0.2 .mu.m due to the limit of the diffraction of light.